The overall goals of this application are to demonstrate that Interleukin-19 (IL-19), a Th2 anti- inflammatory interleukin, can attenuate atherosclerosis, and identify the potential mechanisms of this inhibition. IL-19 is a newly described Th2, (T regulatory) anti-inflammatory interleukin which until our work, had been ascribed to be inflammatory cell-specific. We remain the only laboratory to investigate a role for this interleukin in vascular biology, particularly with respect to EC and VSMC pathophysiology, and to demonstrate molecular mechanisms for these effects. We previously reported that; 1- IL-19 is not detectible in normal artery, but is induced in EC and VSMC in human atherosclerotic lesions; 2- addition of IL-19 to VSMC reduces their migration, proliferation, and abundance of proliferative and inflammatory proteins; 3- IL-19 does NOT inhibit NF-kB, but does reduce the stability of inflammatory and proliferative mRNA transcripts in an HuR-dependent manner; 4- IL-19 induces expression of the vascular and cyto-protective protein Hemeoxygenase-1 (HO-1), and reduces apoptosis induced by vascular reactive oxygen species (ROS) in an HO-1 dependent manner. In this application we present preliminary data showing that addition of recombinant IL-19 to LDLR-/- mice fed an atherogenic diet significantly and dramatically decreases atherosclerotic plaque, and IL-19-/- mice have an exacerbated response to ligation injury. Based on published and preliminary data, we hypothesize that there are multiple, pleiotropic mechanisms for these protective effects, and Specific Aims are designed to test each of these mechanisms. In Aim 1, we will determine if absence of IL-19 exacerbates, and if over expression attenuates atherosclerosis. Aim 2 will test the hypothesis that one mechanism of IL-19 protection is primarily facilitated by adoptive immune system polarization to Th2. Aim 3 will test the hypothesis that IL-19 atheroprotection is mediated by reduction in leukocyte-endothelial cell interaction, and/or IL-19 induction of HO-1 expression. Aim 4 will determine the molecular mechanisms of how IL- 19 decreases inflammatory gene abundance. This application is potentially paradigm-changing as it will implicate a Th2 interleukin as an endogenous cytokine expressed by inflamed vascular cells with multiple autocrine and paracrine dampening effects. It will identify novel molecular mechanisms and targets of anti-inflammatory pathways in these cells.